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Discussion Starter · #1 · (Edited)
i have made a few screens before with no problems, until now. Im trying to make a screen with a thick emulsion coat for white ink on black (1 coat on inside and 3 coats on outside). I did a 1 and 1 coat and let it dry overnight, then a second coat on bottom, let dry 3-4 hours, then a 3rd coat on bottom, it dried under the fan and then was placed into a black bag bag and stored for a few days. I printed what i believe to be a dark transparency, i exposed it for 16 minutes due to the thick emulsion (usually expose for 13 with 1 and 1 coat). When i went to remove transparency it was stuck to emulsion and left bubbles in the emulsion when i finally got it off, during the washout i had to work the pressure cleaner to get it to rinse out to the point the emulsion blew out also, the emulsion came off like latex paint. Did i not let the emulsion dry long enough ?, did i overexpose the screen ?

Sorry about the typo in the title, i guess i cant fix that now !!
 

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Never heard of anyone storing coated screens in a bag before, this could have trapped in moisture, causing your emulsion to become tacky. Even if the screen was dry prior to putting it in the bag.

You want to store your coated screens in a dehumidified room, preferably with good air movement in the room, as moisture is the arch enemy of unexposed emulsion.
 

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Sounds like you over exposed the screen.

What kind of exposure unit do you have? Do you have an overhead Halogen Light on a PVC stand? I don't think you need to expose it for 16 minutes. You also don't need all that emulsion. White ink is thick enough by itself. I would coat on both sides let it dry with a fan, turning it around about 20 minutes after you started to dry it.

It only needs to dry for about 30 minutes. It should be completely dry at that point. If you have a pretty opague image you can tape it on, place a piece of glass on it and turn it on for 13 minutes. Take the glass off, then the film/transparency. Wet both sides of the screen, and let it sit for four minutes. After that wash it out.

I modified my PVC exposure unit with a 500 Watt Halogen Light to expose in 3 minutes. I cut the vertical pvc pipes down so there's only 12 inches from the bottom of the light to the top of the piece of glass. I also used an 1/4" Low E class. I then expose for 3 minutes, and follow the same steps as above.
 

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Discussion Starter · #5 ·
I put the screen into the black bag to keep it from the light until i was ready to expose, i know the ryonet offers a pre coated screen that they ship in a black bag to protect from light, so i assumed this would be a good way to keep it unexposed for a few days. I think that overexposure sound like it may be the problem, the time i came up with was based on the video i received from ryonet which said to add 25-30% to your drying time (standard time i use is 13 min for 1-1 coat) for the thick coat of emulsion which is what they recommended for white ink on dark colors to build a deeper well for the ink. I will retry this without putting it into the bag and try a little less exposure time.
 

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Demj,

I do the same and don't have problems. We live in the North East, and have some of the highest humidity in the country. If I don't need a screen right away, I'll let it dry over night. Many times I dry it, and put it right in the closet and put a bag over it incase I come in and turn the light on.

Remember one thing, UV is what exposes your screen. If you still have incandencent bulbs on the ceiling they probably want expose your screen. It needs to be direct sun light or something with a lot of UV.

When I'm exposing I leave the lights on. If I'm exposing during the day indoors I leave the lights on. The only difference is I pull the drapes closed so I get no direct sun light.

My guess is that you exposed it for too long, and the emulsion was probably a little tacky. Just to make sure next time, after you take the bag off, run the fan on both sides for a few minutes each side.
 

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What it really sounds like is not only overexposure but overheating due to close proximity of your light source and the duration.

You're making a thicker stencil to get a heavier ink deposit. The assumption is to use a coarser mesh. Kinda sorta but not necessarily. The ink layer is controlled more by the stencil thickness and print technique than the mesh count. The mesh count and ink viscosity affects the ease with which he ink passes through the screen (also coupled with set up and technique).

Anyway, the thicker emulsion is going to require more exposure for proper cure but random percentage time estimates are just shots in the dark. Dial it in more accurately with a single step exposure calculator and check the light source distance and how much heat it may be outputting.
 

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Also, with the heavier deposit of emulsion, it's going to take a lot longer for it to completely dry. I think that's why you had the moisture issue and sticking...and yes, probably also the too much heat building up too like Tygeron said.
 

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Discussion Starter · #10 ·
Im going to retry this with a little less time on the exposure, but how would you recommend keeping the heat down, its a 500w halogen bulb on a pvc stand, the bulb is about 17" above the screen (the screen sits with a piece of black foam in the bottom and a piece of 1/8 glass on top). Should i let a fan run on it to dissipate the heat ?
 

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No, if you reduce the time you expose the heat will be less. I think you should chop your vertical PVC pipe so the bottom of the light, and the top of the Glass sitting on your frame are 12 inches apart.

Watch and listen to this video: [media]http://www.youtube.com/watch?v=1OIpRQt9ttY[/media]

This will reduce your exposure time to 3 minutes.
 

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Discussion Starter · #14 ·
So if i lower the light from 16" where it is now down to 12" it should drop by burning time from 13 min. down to 3 min ? Also by lowering it down will it cause a smaller light pattern on the the screen (will there be significantly more light in the center of the screen vs the top and bottom) ? Im figuring the light comes down like an upside down V. also if the standard 1/1 coated screen take 3 minutes any guess on a screen with 3/1 coating ? Sorry for some many questions.
Thanks
 

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Can you upload a picture of your exposure unit so we know what you have?

We use a PVC piping. So, there are two vertical pipes that hold your light up at 16" either buy two new ones at about 13" or cut the ones you have. They just pull out, and you replace them.

I'd just buy new new pvc pipes and replace them. Home Depot sells 2 foot pipes. Just get the right width. Probably 3/4" of an inch thick.

And yes, the exposure time drops to 3 minutes. Try a little patch instead of a whole screen. Make it 3/1 and place one letter in it. Then expose for about 3 minutes and 20 seconds.
 

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Discussion Starter · #16 ·
Can you upload a picture of your exposure unit so we know what you have?

We use a PVC piping. So, there are two vertical pipes that hold your light up at 16" either buy two new ones at about 13" or cut the ones you have. They just pull out, and you replace them.

I'd just buy new new pvc pipes and replace them. Home Depot sells 2 foot pipes. Just get the right width. Probably 3/4" of an inch thick.

And yes, the exposure time drops to 3 minutes. Try a little patch instead of a whole screen. Make it 3/1 and place one letter in it. Then expose for about 3 minutes and 20 seconds.
ill give that a try tomorrow, i have the pvc stand from ryonet, sounds the same as you described.
 

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Discussion Starter · #18 ·
Failure once again, i moved the light so its 12" from glass and exposed for 3min 30 sec. and once again no luck, a few areas that did wash out are nice and thick. As soon as i gave it a rinse on both sides with the house i got what i think is emulsion or diazo streaks, on the squeegee side when it was tilted forward i noticed a yellowish water sitting in the groove at bottom of screen. I tried rinsing the back part way through and the emulsion just came off. Also the transparency stuck to the screen again. I did some temp measurement before the 13 min exposure from 16" was 190, the 16min exposure went up to 200. and 3.5 min was 150. I attached a few photos and a short video, if anyone could take a look and see what you think. Im going to order the step exposure strip to help, but right now im ready to give up on making a 3/1 screen.

[media]http://www.youtube.com/watch?v=2rxbcBe-AWY[/media]Sorry for the camera not being on the screen the whole time
 

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i think you gue a missing the fact that he/she is using dual cure emulsion from ryonet... i on beleve that stuff will ever cure in minutes! and quite honestly i tried the same process as the op with the same equipment and have never had luck. i just do 2 wet coats on the shirt side and 1 on the squeegee side and let 'er rip. i see where having a thinker coat of emulsion makes very good sense but i have also found that with enough practice or a print flash print you can print whites just as good with a 1/1 coat
 

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Demj,

One, when you wash out the screen you have to spray water on both sides and let it sit for 4 minutes wet. Give it a good washing of water first.

Then come back and wash out your screen. In fact, wash both sides. The harder it is to wash out, means you exposed to long.

Do one at 3 minutes. Instead of coating the whole schreen, just do a 4 inch by 4 inch patch. After it dries, place a dark black letter or even a 2 inch square. Expose that for 3 minutes. Originally I said 3 minutes and 20 seconds. That was to make up for a thicker screen. You exposed for 3 minutes an 30 seconds.

Once you figure out the time, then switch to coating a full screen, and exposing for whatever time worked.

Will you make a video of you coating the screen so we can see what you're doing?

It looks close. If you didn't reclaim the screen try washing for a little longer.

Demj, Is your Film sitting on top of the Glass or Between the glass and screen?
 
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